1. Field of the Invention
The present invention relates to an imaging device having an imaging element including at least three types of color detection photoelectric conversion elements for detecting different color components of light and brightness detection photoelectric conversion elements for detecting a brightness component of light.
2. Description of the Related Art
A hitherto-proposed imaging element includes a brightness detection photoelectric conversion element having a brightness filter formed on a light-receiving surface of the element; an R photoelectric conversion element having an R color filter that is formed on the light-receiving surface of the element and that allows transmission of a red (R) color component of light; a G photoelectric conversion element having a G color filter that is formed on the light-receiving surface of the element and that allows transmission of a green (G) color component of light; and a B photoelectric conversion element having a B color filter that is formed on the light-receiving surface of the element and that allows transmission of a blue (B) color component of light (see JP-A-2003-318375).
There is conceived an example in which the brightness filter of the imaging element is not provided at all at a position above the light-receiving surface of the brightness detection photoelectric conversion element. In this case, the sensitivity of signals acquired from the respective photoelectric conversion elements is as shown on the left side of FIG. 8. Since the brightness filter permits transmission of all components of light, signals from the brightness detection photoelectric conversion elements are indicated as W (white). Since the filter is not present on the light-receiving surface, the sensitivity of the signals W from the brightness detection photoelectric conversion elements is maximum. Further, the sensitivity of a G signal is generally higher than sensitivities of R and B signals. Hence, as illustrated, the sensitivities exhibit a relationship of W>G>R>B.
When a white balance of a signal acquired from the imaging element is adjusted, a level must be matched with the sensitivity of any of the signals in order to compensate for a difference among sensitivities of the signals. In consideration of color reproducibility, the G signal is generally taken as a reference. As shown on the right side of FIG. 8, the R signal, the B signal, and the W signal are multiplied by a gain so as to match with the C signal, saturation levels of the R and B signals become greater by an amount corresponding to the gain multiplied because saturation levels of the respective photoelectric conversion elements are identical. However, the saturation level of the W signal becomes smaller by an amount corresponding to the gain multiplied.